Implantable therapy system

ABSTRACT

A therapy system for applying an electrical signal to an internal anatomical feature of a patient includes an implantable component and an external component. The implantable component is configured to receive a selected therapy program and a selected therapy schedule from the external component. The implantable component is adapted to be selectively configured into one of a training mode and a delivery mode. The implantable component is configured to apply therapy to the internal anatomical feature in accordance with the selected therapy program and the selected therapy schedule when configured in the delivery mode. The implantable component is configured to simulate application of therapy when configured in the training mode.

CROSS REFERENCE

This application claims priority to U.S. Provisional Application Ser.No. 60/941,118, filed May 31, 2007, and entitled “IMPLANTABLE DEVICE,”the disclosure of which is hereby incorporated by reference herein.

This application discloses and claims subject matter disclosed incommonly assigned U.S. application Ser. Nos. ______ and ______ (attorneydocket numbers 14283.0034USU1 and 14283.0034USU2, respectively), filedconcurrently herewith and titled “Implantable Therapy System” and“Therapy System,” respectively. U.S. application Ser. No. ______ (havingattorney docket number 14283.0034USU1) names Adrianus Donders, MarkRaymond Stultz, and Koen Jacob Weijand as inventors; and U.S.application Ser. No. ______ (having attorney docket number14283.0034USU2) names Mark Raymond Stultz as an inventor.

I. BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention pertains to systems for applying electrical signals to ananatomical feature of a patient. While many of the disclosed conceptsare applicable to a wide variety of therapies (e.g., cardiac pacing withelectrodes applied to heart tissue), the invention is described in apreferred embodiment where the invention pertains to the treatment ofgastro-intestinal disorders such as obesity, pancreatitis, irritablebowel syndrome and inflammatory disorders. In a most preferredembodiment, this invention pertains to the treatment of agastrointestinal disorder by the application of a high frequency signalto a vagus nerve of a patient.

2. Description of the Prior Art

A blocking therapy can be used alone or in combination with traditionalelectrical nerve stimulation in which impulses are created forpropagation along a nerve. The disorders to be treated include, withoutlimitation, functional gastrointestinal disorders (FGIDs) (such asfunctional dyspepsia (dysmotility-like) and irritable bowel syndrome(IBS)), gastroparesis, gastroesophageal reflux disease (GERD),inflammation, discomfort and other disorders.

In a blocking therapy, an electrode (or multiple electrodes) is placedon or near a vagus nerve or nerves of a patient. By “near”, it is meantclose enough that a field created by the electrode captures the nerve.As disclosed in the foregoing patent and applications, the electrode canbe placed directly on a nerve, overlying tissue surrounding a nerve oron or in an organ near a nerve.

Higher frequencies (e.g., 2,500 Hz-20,000 Hz) are believed to result inmore consistent neural conduction block. Particularly, the nerveconduction block is applied with an electrical signal selected to blockthe entire cross-section of the nerve (e.g., both afferent and efferentsignals on both myelinated and non-myelinated fibers) at the site ofapplication of the blocking signal.

In one embodiment of the electrodes a signal amplitude of 0.5 mA to 8 mAat the electrode-nerve interface has been found to be adequate forblocking. However, depending on electrode design, other amplitudes maysuffice. Other signal parameters, as non-limiting examples, include anadjustable pulse width (e.g., 50 μsec to 500 μsec), and a frequencyrange of (by non-limiting example) 1000 Hz to 10,000 Hz. It must berecognized that the frequency sets certain limitations on the availablepulse width; for example, the pulse width cannot exceed 50% of the cycletime for a symmetrical biphasic pulse.

A typical duty cycle of therapy could consist of 5 minutes on and 10minutes off. These are representative only. For example, a duty cyclecould be 2 minutes on and 5 minutes off or be 30 minutes on per day.These examples are given to illustrate the wide latitude available inselecting particular signal parameters for a particular patient.

A complete system for applying a signal to a nerve may include systemsfor addressing the potential for charge build-up, assuring goodcommunication between implanted and external components, rechargingimplantable batteries, physician and patient controls and programmingand communication with the system. These issues and selected prior artsystems for addressing these issues will now be discussed.

II. SUMMARY OF THE INVENTION

According to a preferred embodiment of the present invention, a therapysystem is disclosed for applying therapy to an internal anatomicalfeature of a patient. The system includes at least one electrode forimplantation within the patient and placement at the anatomical feature(e.g., a nerve) for applying the therapy signal to the feature uponapplication of a treatment signal to the electrode. An implantablecomponent is placed in the patient's body beneath a skin layer andcoupled to the electrode. The implantable component includes animplanted antenna. An external component has an external antenna forplacement above the skin and adapted to be electrically coupled to theimplanted antenna across the skin through radiofrequency transmission.

According to aspects, the external component is adapted to be configuredinto multiple selectable operating modes including an operating roommode, a programming mode, and a charging mode.

For example, communicatively coupling the external component toperipheral devices can automatically configure the external componentinto one of the operating modes.

According to other aspects, the implantable component is adapted to beconfigured into multiple selectable operating modes including a trainingmode for simulating a therapy, and a therapy mode for providing therapy.

According to other aspects, the implantable component may be configuredto increment therapy settings automatically by a predetermined amountafter a predetermined period of time.

III. BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic representation of a therapy system having featuresthat are examples of inventive aspects of the principles of the presentinvention, the therapy system including a neuroregulator and an externalcharger;

FIG. 2A is a plan view of an implantable neuroregulator for use in thetherapy system of FIG. 1 according to aspects of the present disclosure;

FIG. 2B is a plan view of another implantable neuroregulator for use inthe therapy system of FIG. 1 according to aspects of the presentdisclosure.

FIG. 3A is a block diagram of a representative circuit module for theneuroregulator of FIG. 2A and FIG. 2B according to aspects of thepresent disclosure;

FIG. 3B is a block diagram of another representative circuit module forthe neuroregulator of FIG. 2A and FIG. 2B according to aspects of thepresent disclosure;

FIG. 4 is a block diagram of a circuit module for an external chargerfor use in the therapy system of FIG. 1 according to aspects of thepresent disclosure;

FIG. 5 is a plan schematic view of an example external charger for usein the therapy system of FIG. 1 according to aspects of the presentdisclosure;

FIG. 6 is a plan, schematic view of an external charger and schematicviews of a patient transmit coil and a physician transmit coilconfigured to couple to the external charger according to aspects of thepresent disclosure;

FIG. 7 is a side elevation, schematic view of an external coil in adesired alignment over an implanted coil according to aspects of thepresent disclosure;

FIG. 8 illustrates the external coil and implanted coil of FIG. 7arranged in a misaligned position according to aspects of the presentdisclosure;

FIG. 9 is a perspective view of a distal portion of a bipolar therapylead according to aspects of the present disclosure;

FIG. 10 is a schematic representation of an electrode placement for ablocking therapy according to aspects of the present disclosure;

FIG. 11 is a schematic representation of a first electrode configurationaccording to aspects of the present disclosure;

FIG. 12 is a schematic representation of a typical waveform according toaspects of the present disclosure;

FIG. 13 is a schematic representation of a second electrodeconfiguration according to aspects of the present disclosure;

FIG. 14 is a schematic representation of a typical waveform according toaspects of the present disclosure;

FIG. 15 is a schematic representation of a third electrode configurationaccording to aspects of the present disclosure;

FIG. 16 is a schematic representation of a typical waveform according toaspects of the present disclosure;

FIG. 17 is a schematic representation of a fourth electrodeconfiguration according to aspects of the present disclosure;

FIG. 18 is a schematic representation of a typical waveform according toaspects of the present disclosure;

FIG. 19 is a graphical illustration of a treatment schedule according toaspects of the present disclosure;

FIG. 20 is a schematic representation of a signal pulse illustratingcharge balancing according to aspects of the present disclosure;

FIG. 21 is a schematic representation of an alternative means of chargebalancing according to aspects of the present disclosure;

FIG. 22 is a schematic illustration of a charge balancing system shownin a shorting state according to aspects of the present disclosure;

FIG. 23 is the view of FIG. 22 in a non-shorting state according toaspects of the present disclosure; and

FIG. 24 is a graphical illustration comparing waveforms in shorting andnon-shorting states according to aspects of the present disclosure.

IV. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

With reference now to the various drawing figures in which identicalelements are numbered identically throughout, a description of thepreferred embodiments of the present invention will now be described.While the invention is applicable to treating a wide variety ofgastro-intestinal disorders, the invention will be described inpreferred embodiments for the treatment of obesity.

FIG. 1 schematically illustrates a therapy system 100 for treatingobesity or other gastro-intestinal disorders. The therapy system 100includes a neuroregulator 104, an electrical lead arrangement 108, andan external charger 101. The neuroregulator 104 is adapted forimplantation within a patient to be treated for obesity. As will be morefully described herein, the neuroregulator 104 typically is implantedjust beneath a skin layer 103.

The neuroregulator 104 is configured to connect electrically to the leadarrangement 108. In general, the lead arrangement 108 includes two ormore electrical lead assemblies 106, 106 a. In the example shown, thelead arrangement 108 includes two identical (bipolar) electrical leadassemblies 106, 106 a. The neuroregulator 104 generates therapy signalsand transmits the therapy signals to the lead assemblies 106, 106 a.

The lead assemblies 106, 106 a up-regulate and/or down-regulate nervesof a patient based on the therapy signals provided by the neuroregulator104. In an embodiment, the lead assemblies 106, 106 a include distalelectrodes 212, 212 a, which are placed on one or more nerves of apatient. For example, the electrodes 212, 212 a may be individuallyplaced on the anterior vagal nerve AVN and posterior vagal nerve PVN,respectively, of a patient. For example, the distal electrodes 212, 212a can be placed just below the patient's diaphragm. In otherembodiments, however, fewer or more electrodes can be placed on or nearfewer or more nerves.

The external charger 101 includes circuitry for communicating with theimplanted neuroregulator 104. In general, the communication istransmitted across the skin 103 along a two-way signal path as indicatedby arrows A. Example communication signals transmitted between theexternal charger 101 and the neuroregulator 104 include treatmentinstructions, patient data, and other signals as will be describedherein. Energy also can be transmitted from the external charger 101 tothe neuroregulator 104 as will be described herein.

In the example shown, the external charger 101 can communicate with theimplanted neuroregulator 104 via bidirectional telemetry (e.g. viaradiofrequency (RF) signals). The external charger 101 shown in FIG. 1includes a coil 102, which can send and receive RF signals. A similarcoil 105 can be implanted within the patient and coupled to theneuroregulator 104. In an embodiment, the coil 105 is integral with theneuroregulator 104. The coil 105 serves to receive and transmit signalsfrom and to the coil 102 of the external charger 101.

For example, the external charger 101 can encode the information as abit stream by amplitude modulating or frequency modulating an RF carrierwave. The signals transmitted between the coils 102, 105 preferably havea carrier frequency of about 6.78 MHz. For example, during aninformation communication phase, the value of a parameter can betransmitted by toggling a rectification level between half-waverectification and no rectification. In other embodiments, however,higher or lower carrier wave frequencies may be used.

In an embodiment, the neuroregulator 104 communicates with the externalcharger 101 using load shifting (e.g., modification of the load inducedon the external charger 101). This change in the load can be sensed bythe inductively coupled external charger 101. In other embodiments,however, the neuroregulator 104 and external charger 101 can communicateusing other types of signals.

In an embodiment, the neuroregulator 104 receives power to generate thetherapy signals from an implantable power source 151 (see FIG. 3A), suchas a battery. In a preferred embodiment, the power source 151 is arechargeable battery. In some embodiments, the power source 151 canprovide power to the implanted neuroregulator 104 when the externalcharger 101 is not connected. In other embodiments, the external charger101 also can be configured to provide for periodic recharging of theinternal power source 151 of the neuroregulator 104. In an alternativeembodiment, however, the neuroregulator 104 can entirely depend uponpower received from an external source (see FIG. 3B). For example, theexternal charger 101 can transmit power to the neuroregulator 104 viathe RF link (e.g., between coils 102, 105).

In some embodiments, the neuroregulator 104 initiates the generation andtransmission of therapy signals to the lead assemblies 106, 106 a. In anembodiment, the neuroregulator 104 initiates therapy when powered by theinternal battery 151. In other embodiments, however, the externalcharger 101 triggers the neuroregulator 104 to begin generating therapysignals. After receiving initiation signals from the external charger101, the neuroregulator 104 generates the therapy signals (e.g., pacingsignals) and transmits the therapy signals to the lead assemblies 106,106 a.

In other embodiments, the external charger 101 also can provide theinstructions according to which the therapy signals are generated (e.g.,pulse-width, amplitude, and other such parameters). In a preferredembodiment, the external charger 101 includes memory in which severalpredetermined programs/therapy schedules can be stored for transmissionto the neuroregulator 104. The external charger 101 also can enable auser to select a program/therapy schedule stored in memory fortransmission to the neuroregulator 104. In another embodiment, theexternal charger 101 can provide treatment instructions with eachinitiation signal.

Typically, each of the programs/therapy schedules stored on the externalcharger 101 can be adjusted by a physician to suit the individual needsof the patient. For example, a computing device (e.g., a notebookcomputer, a personal computer, etc.) 107 can be communicativelyconnected to the external charger 101. With such a connectionestablished, a physician can use the computing device 107 to programtherapies into the external charger 101 for either storage ortransmission to the neuroregulator 104.

The neuroregulator 104 also may include memory 152 (see FIGS. 3A and 3B)in which treatment instructions and/or patient data can be stored. Forexample, the neuroregulator 104 can store therapy programs indicatingwhat therapy should be delivered to the patient. The neuroregulator 104also can store patient data indicating how the patient utilized thetherapy system 100 and/or reacted to the delivered therapy.

In what follows, the focus of the detailed description is the preferredembodiment in which the neuroregulator 104 contains a rechargeablebattery 151 from which the neuroregulator 104 may draw power (FIG. 3A).

1. System Hardware Components

a. Neuroregulator

Different embodiments of the neuroregulator 104, 104′ are illustratedschematically in FIGS. 2A and 2B, respectively. The neuroregulator 104,104′ is configured to be implanted subcutaneously within the body of apatient. Preferably, the neuroregulator 104, 104′ is implantedsubcutaneously on the thoracic sidewall in the area slightly anterior tothe axial line and caudal to the arm pit. In other embodiments,alternative implantation locations may be determined by the implantingsurgeon.

The neuroregulator 104, 104′ is generally sized for such implantation inthe human body. By way of non-limiting example, an outer diameter D, D′of the neuroregulator 104, 104′ is typically less than or equal to aboutsixty mm and a thickness of the neuroregulator 104, 104′ is less than orequal to about fifteen mm. In a preferred embodiment, the neuroregulator104, 104′ has a maximum outer diameter D, D′ of about fifty-five mm anda maximum thickness of about nine mm. In one embodiment, theneuroregulator 104, 104′ weighs less than about one hundred twentygrams.

Typically, the neuroregulator 104, 104′ is implanted parallel to theskin surface to maximize RF coupling efficiency with the externalcharger 101. In an embodiment, to facilitate optimal information andpower transfer between the internal coil 105, 105′ of the neuroregulator104, 104′ and the external coil 102 of the external charger 101, thepatient can ascertain the position of the neuroregulator 104, 104′(e.g., through palpation or with the help of a fixed marking on theskin). In an embodiment, the external charger 101 can facilitate coilpositioning as discussed herein with reference to FIGS. 7 and 8.

As shown in FIGS. 2A and 2B, the neuroregulator 104, 104′ generallyincludes a housing 109, 109′ overmolded with the internal coil 105,105′, respectively. The overmold 110, 110′ of the neuroregulator 104,104′ is formed from a bio-compatible material that is transmissive to RFsignals (i.e., or other such communication signals). Some suchbio-compatible materials are well known in the art. For example, theovermold 110, 110′ of the neuroregulator 104, 104′ may be formed fromsilicone rubber or other suitable materials. The overmold 110, 110′ alsocan include suture tabs or holes 119, 119′ to facilitate placementwithin the patient's body.

The housing 109, 109′ of the neuroregulator 104, 104′ also may contain acircuit module, such as circuit 112 (see FIGS. 1, 3A, and 3B), to whichthe coil 105, 105′ may be electrically connected along a path 105 a, 105a′. The circuit module within the housing 109 may be electricallyconnected to the lead assemblies 106, 106 a (FIG. 1) through conductors114, 114 a. In the example shown in FIG. 2A, the conductors 114, 114 aextend out of the housing 109 through strain reliefs 118, 118 a. Suchconductors 114, 114 a are well known in the art.

The conductors 114, 114 a terminate at connectors 122, 122 a, which areconfigured to receive or otherwise connect the lead assemblies 106, 106a (FIG. 1) to the conductors 114, 114 a. By providing connectors 122,122 a between the neuroregulator 104 and the lead assemblies 106, 106 a,the lead assemblies 106, 106 a may be implanted separately from theneuroregulator 104. Also, following implantation, the lead assemblies106, 106 a may be left in place while the originally implantedneuroregulator 104 is replaced by a different neuroregulator.

As shown in FIG. 2A, the neuroregulator connectors 122, 122 a can beconfigured to receive connectors 126 of the lead assemblies 106, 106 a.For example, the connectors 122, 122 a of the neuroregulator 104 may beconfigured to receive pin connectors (not shown) of the lead assemblies106, 106 a. In another embodiment, the connectors 122, 122 a may beconfigured to secure to the lead assemblies 106, 106 a using set-screws123, 123 a, respectively, or other such fasteners. In a preferredembodiment, the connectors 122, 122 a are well-known IS-1 connectors. Asused herein, the term “IS-1” refers to a connector standard used by thecardiac pacing industry, and is governed by the international standardISO 5841-3.

In the example shown in FIG. 2B, female connectors 122′, 122 a′configured to receive the leads 106, 106 a are molded into a portion ofthe overmold 110′ of the neuroregulator 104′. The leads connectors 126are inserted into these molded connectors 122′, 122 a′ and secured viasetscrews 123′, 123 a′, seals (e.g., Bal Seals®), and/or anotherfastener.

The circuit module 112 (see FIGS. 1, 3A, and 3B) is generally configuredto generate therapy signals and to transmit the therapy signals to thelead assemblies 106, 106 a. The circuit module 112 also may beconfigured to receive power and/or data transmissions from the externalcharger 101 via the internal coil 105. The internal coil 105 may beconfigured to send the power received from the external charger to thecircuit module 112 for use or to the internal power source (e.g.,battery) 151 of the neuroregulator 104 to recharge the power source 151.

Block diagrams of example circuit modules 112, 112″ are shown in FIGS.3A, 3B, respectively. Either circuit module 112, 112″ can be utilizedwith any neuroregulator, such as neuroregulators 104, 104′ describedabove. The circuit modules 112, 112″ differ in that the circuit module112 includes an internal power source 151 and a charge control module153 and the circuit module 112″ does not. Accordingly, power foroperation of the circuit module 112″ is provided entirely by theexternal charger 101 via the internal coil 105. Power operation forcircuit module 112 may be provided by the external charger 101 or by theinternal power source 151. Either circuit module 112, 112″ may be usedwith either neuroregulator 104, 104′ shown in FIGS. 2A, 2B. For ease inunderstanding, the following description will focus on the circuitmodule 112 shown in FIG. 3A.

The circuit module 112 includes an RF input 157 including a rectifier164. The rectifier 164 converts the RF power received from the internalcoil 105 into DC electric current. For example, the RF input 157 mayreceive the RF power from the internal coil 105, rectify the RF power toa DC power, and transmit the DC current to the internal power source 151for storage. In one embodiment, the RF input 157 and the coil 105 may betuned such that the natural frequency maximizes the power transferredfrom the external charger 101.

In an embodiment, the RF input 157 can first transmit the received powerto a charge control module 153. The charge control module 153 receivespower from the RF input 157 and delivers the power where needed througha power regulator 156. For example, the RF input 157 may forward thepower to the battery 151 for charging or to circuitry for use increating therapy signals as will be described below. When no power isreceived from the coil 105, the charge control 153 may draw power fromthe battery 151 and transmit the power through the power regulator 160for use. For example, a central processing unit (CPU) 154 of theneuroregulator 104 may manage the charge control module 153 to determinewhether power obtained from the coil 105 should be used to recharge thepower source 151 or whether the power should be used to produce therapysignals. The CPU 154 also may determine when the power stored in thepower source 151 should be used to produce therapy signals.

The transmission of energy and data via RF/inductive coupling is wellknown in the art. Further details describing recharging a battery via anRF/inductive coupling and controlling the proportion of energy obtainedfrom the battery with energy obtained via inductive coupling can befound in the following references, all of which are hereby incorporatedby reference herein: U.S. Pat. No. 3,727,616, issued Apr. 17, 1973, U.S.Pat. No. 4,612,934, issued Sep. 23, 1986, U.S. Pat. No. 4,793,353,issued Dec. 27, 1988, U.S. Pat. No. 5,279,292, issued Jan. 18, 1994, andU.S. Pat. No. 5,733,313, issued Mar. 31, 1998.

In general, the internal coil 105 may be configured to pass datatransmissions between the external charger 101 and a telemetry module155 of the neuroregulator 104. The telemetry module 155 generallyconverts the modulated signals received from the external charger 101into data signals understandable to the CPU 154 of the neuroregulator104. For example, the telemetry module 155 may demodulate an amplitudemodulated carrier wave to obtain a data signal. In one embodiment, thesignals received from the internal coil 105 are programming instructionsfrom a physician (e.g., provided at the time of implant or on subsequentfollow-up visits). The telemetry module 155 also may receive signals(e.g., patient data signals) from the CPU 154 and may send the datasignals to the internal coil 105 for transmission to the externalcharger 101.

The CPU 154 may store operating parameters and data signals received atthe neuroregulator 104 in an optional memory 152 of the neuroregulator104. Typically, the memory 152 includes non-volatile memory. In otherembodiments, the memory 152 also can store serial numbers and/or modelnumbers of the leads 106; serial number, model number, and/or firmwarerevision number of the external charger 101; and/or a serial number,model number, and/or firmware revision number of the neuroregulator 104.

The CPU 154 of the neuroregulator 104 also may receive input signals andproduce output signals to control a signal generation module 159 of theneuroregulator 104. Signal generation timing may be communicated to theCPU 154 from the external charger 101 via the coil 105 and the telemetrymodule 155. In other embodiments, the signal generation timing may beprovided to the CPU 154 from an oscillator module (not shown). The CPU154 also may receive scheduling signals from a clock, such as 32 KHzreal time clock (not shown).

The CPU 154 forwards the timing signals to the signal generation module159 when therapy signals are to be produced. The CPU 154 also mayforward information about the configuration of the electrode arrangement108 to the signal generation module 159. For example, the CPU 154 canforward information obtained from the external charger 101 via the coil105 and the telemetry module 155.

The signal generation module 159 provides control signals to an outputmodule 161 to produce therapy signals. In an embodiment, the controlsignals are based at least in part on the timing signals received fromthe CPU 154. The control signals also can be based on the electrodeconfiguration information received from the CPU 154.

The output module 161 produces the therapy signals based on the controlsignals received from the signal generation module 159. In anembodiment, the output module 161 produces the therapy signals byamplifying the control signals. The output module 161 then forwards thetherapy signals to the lead arrangement 108.

In an embodiment, the signal generation module 159 receives power via afirst power regulator 156. The power regulator 156 regulates the voltageof the power to a predetermined voltage appropriate for driving thesignal generation module 159. For example, the power regulator 156 canregulate the voltage to about 2.5 volts.

In an embodiment, the output module 161 receives power via a secondpower regulator 160. The second power regulator 160 may regulate thevoltage of the power in response to instructions from the CPU 154 toachieve specified constant current levels. The second power regulator160 also may provide the voltage necessary to deliver constant currentto the output module 161.

The output module 161 can measures the voltage of the therapy signalsbeing outputted to the lead arrangement 108 and reports the measuredvoltage to the CPU 154. A capacitive divider 162 may be provided toscale the voltage measurement to a level compatible with the CPU 154. Inanother embodiment, the output module 161 can measure the impedance ofthe lead arrangement 108 to determine whether the leads 106, 106 a arein contact with tissue. This impedance measurement also may be reportedto the CPU 154.

b. External Charger

A block diagram view of an example external charger 101 is shown in FIG.4. The example external charger 101 may cooperate with any of theneuroregulators 104, 104′ discussed above to provide therapy to apatient. The external charger 101 is configured to transmit to theneuroregulator 104 (e.g., via an RF link) desired therapy parameters andtreatment schedules and to receive data (e.g., patient data) from theneuroregulator 104. The external charger 101 also is configured totransmit energy to the neuroregulator 104 to power the generation oftherapy signals and/or to recharge an internal battery 151 of theneuroregulator 104. The external charger 101 also can communicate withan external computer 107.

In general, the external charger 101 includes power and communicationscircuitry 170. The power and communications circuitry 170 is configuredto accept input from multiple sources, to process the input at a centralprocessing unit (CPU) 200, and to output data and/or energy (e.g., viacoil 102, socket 174, or display 172). It will be appreciated that it iswell within the skill of one of ordinary skill in the art (having thebenefit of the teachings of the present invention) to create suchcircuit components with such function.

For example, the circuit power and communications circuit 170 can beelectrically connected to the external coil 102 for inductive electricalcoupling to the coil 105 of the neuroregulator 104. The power andcommunications circuit 170 also can be coupled to interface componentsenabling input from the patient or an external computing device (e.g., apersonal computer, a laptop, a personal digital assistant, etc.) 107.For example, the external charger 101 can communicate with the computingdevice 107 via an electrically isolated Serial port.

The external charger 101 also includes a memory or data storage module181 in which data received from the neuroregulator 104 (e.g., via coil102 and socket input 176), the external computer 107 (e.g., via socketinput 174), and/or the patient (e.g. via select input 178) can bestored. For example, the memory 181 can store one or more predeterminedtherapy programs and/or therapy schedules provided from the externalcomputer 107. The memory 181 also can store software to operate theexternal charger 101 (e.g., to connect to the external computer 107, toprogram external operating parameters, to transmit data/energy to theneuroregulator 104, and/or to upgrades the operations of the CPU 200).Alternatively, the external charger 101 can include firmware to providethese functions. The memory 181 also can store diagnostic information,e.g., software and hardware error conditions.

An external computer or programmer 107 may connect to the communicationscircuit 170 through the first input 174. In an embodiment, the firstinput 174 is a port or socket into which a cable coupled to the externalcomputer 107 can be plugged. In other embodiments, however, the firstinput 174 may include any connection mechanism capable of connecting theexternal computer 107 to the external charger 101. The external computer107 provides an interface between the external charger 101 and aphysician (e.g., or other medical professional) to enable the physicianto program therapies into the external charger 101, to run diagnosticand system tests, and to retrieve data from the external charger 101.

The second input 176 permits the external charger 101 to coupleselectively to one of either an external power source 180 or theexternal coil 102 (see FIG. 1). For example, the second input 176 candefine a socket or port into which the power source 180 or external coil102 can plug. In other embodiments, however, the second input 176 can beconfigured to couple to a cable or other coupling device via any desiredconnection mechanism. In one embodiment, the external charger 101 doesnot simultaneously connect to both the coil 102 and the external powersource 180. Accordingly, in such an embodiment, the external powersource 180 does not connect directly to the implanted neuroregulator104.

The external power source 180 can provide power to the external charger101 via the second input 176 when the external charger 101 is notcoupled to the coil 102. In an embodiment, the external power source 180enables the external charger 101 to process therapy programs andschedules. In another embodiment, the external power source 180 suppliespower to enable the external charger 101 to communicate with theexternal computer 107 (see FIG. 1).

The external charger 101 optionally may include a battery, capacitor, orother storage device 182 (FIG. 4) enclosed within the external charger101 that can supply power to the CPU 200 (e.g., when the externalcharger 101 is disconnected from the external power source 180). Thepower and communications circuit 170 can include a power regulator 192configured to receive power from the battery 182, to regulate thevoltage, and to direct the voltage to the CPU 200. In a preferredembodiment, the power regulator 192 sends a 2.5 volt signal to the CPU200.

The battery 182 also can supply power to operate the external coil 102when the coil 102 is coupled to the external charger 101. The battery182 also can supply power to enable the external charger 101 tocommunicate with the external computer 107 when the external powersource 180 is disconnected from the external charger 101. An indicator190 may provide a visual or auditory indication of the remaining powerin the battery 182 to the user.

In an embodiment, the battery 182 of the external charger 101 isrechargeable. For example, the external power source 180 may couple tothe external charger 101 to supply a voltage to the battery 182. In suchan embodiment, the external charger 101 then can be disconnected fromthe external power source 180 and connected to the external coil 102 totransmit power and/or data to the neuroregulator 104. Further detailsregarding example rechargeable systems include U.S. Pat. No. 6,516,227to Meadows, issued Feb. 4, 2003; U.S. Pat. No. 6,895,280 to Meadows,issued May 17, 2005; and U.S. patent application Publication No. US2005/0107841 to Meadows May 19, 2005, the disclosures of which arehereby incorporated herein by reference.

In an alternative embodiment, the battery 180 is a replaceable,rechargeable battery, which is recharged external to the externalcharger 101 in its own recharging stand. In yet another embodiment, thebattery 182 in the external charger 101 can be a replaceable,non-rechargeable battery.

In use, energy from the external power source 180 flows through thesecond input 176 to an energy transfer module 199 of the power andcommunications circuit 170. The energy transfer module 199 directs theenergy either to the CPU 200 to power the internal processing of theexternal charger 101 or to the battery 182. In an embodiment, the energytransfer module 199 first directs the energy to a power regulator 194,which can regulate the voltage of the energy signal before sending theenergy to the battery 182.

In some embodiments, the external coil 102 of the external charger 101can supply energy from the battery 182 to the internal coil 105 of theneuroregulator 104 (e.g., to recharge the internal power source 151(FIG. 3) of the neuroregulator 104). In such embodiments, the energytransfer module 199 receives power from the battery 182 via the powerregulator 194. For example, the power regulator 194 can provide asufficient voltage to activate the energy transfer module 199. Theenergy transfer module 199 also can receive instructions from the CPU200 regarding when to obtain power from the battery 182 and/or when toforward power to the external coil 102. The energy transfer module 199delivers the energy received from the battery 182 to the coil 102 of theexternal charger 101 in accordance with the instructions provided by theCPU 200. The energy is sent from the external coil 102 to the internalcoil 105 of the neuroregulator 104 via RF signals or any other desiredpower transfer signal. In an embodiment, therapy delivery at theneuroregulator 104 is suspended and power is delivered from the externalcharger 101 during recharging of the internal power source 151.

In some embodiments, the external charger 101 controls when the internalbattery 151 of the implanted neuroregulator 104 is recharged. Forexample, the external charger 101 can determine when to recharge thebattery 151 using the processes described in U.S. Pat. No. 6,895,280 toMeadows issued May 17, the disclosure of which is hereby incorporatedherein by reference. In other embodiments, however, the implantedneuroregulator 104 controls when the battery 151 is recharged. Detailspertaining to controlling the battery recharging process can be found inU.S. Pat. No. 3,942,535 to Schulman, issued Mar. 9, 1976; U.S. Pat. No.4,082,097 to Mann, issued Apr. 4, 1978; U.S. Pat. No. 5,279,292 toBaumann, issued Apr. 4, 1978; and U.S. Pat. No. 6,516,227 to Meadows,issued Feb. 4, 2003, the disclosures of which are hereby incorporatedherein by reference. These details typically parallel the batterymanufacturer's recommendations regarding how to charge the battery.

As noted above, in addition to power transmissions, the external coil102 also can be configured to receive data from and to transmitprogramming instructions to the neuroregulator 104 (e.g., via an RFlink). A data transfer module 196 may receive and transmit data andinstructions between the CPU 200 and the internal coil 105. In anembodiment, the programming instructions include therapy schedules andparameter settings. Further examples of instructions and datatransmitted between the external coil 102 and the implanted coil 105 arediscussed in greater detail herein.

FIG. 5 shows a front view of an example external charger 101. Theexternal charger 101 includes a housing 171 defining a first input(e.g., socket input) 174, a second input (e.g., socket input) 176, and athird input (e.g., select input) 178 coupled to the communicationscircuit 170. In an embodiment, the housing 171 also may enclose abattery 182 configured to supply power to the external charger 101 viathe power and communications circuit 170. Alternatively, the externalcharger 101 can receive power from an external source 180 (FIG. 1).

As shown in FIG. 5, visual display 172 also is provided on the housing171 for presenting human readable information processed by thecommunications circuit 170. In an embodiment, the visual display 172 isa liquid crystal display (LCD) screen. In other embodiments, however,the visual display 172 can include any display mechanism (e.g., alight-emitting diode (LED) screen, vacuum fluorescent display (VFD)screen, etc.). Non-limiting examples of information that can be shown onthe visual display 172 include the status of the battery 182 of theexternal charger 101, the status of the battery 151 in the implantedneuroregulator 104, coil position (as will be described), impedancesbetween the electrodes 212, 212 a and attached tissue, and errorconditions.

As shown in FIG. 5, the third input 178 of the external charger 101includes a selection input 178 with which the user can interact with theexternal charger 101. In an embodiment, the selection input 178 caninclude a button, which sequentially selects menu options for variousoperations performed by the external charger 101 when pressedsuccessively. In other embodiments, however, the third input 178includes another type of selection input (e.g., a touch screen, atoggle-switch, a microphone for accepting voice-activated commands,etc.).

Example functions capable of selection by the user include device reset,interrogation of battery status, interrogation of coil position, and/orinterrogation of lead/tissue impedance. In other embodiments, a useralso can select measurement of tissue/lead impedance and/or initiationof a stomach contraction test. Typically, the measurement and testingoperations are performed when the patient is located in an operatingroom, doctor's office, or is otherwise surrounded by medical personnel.

In another embodiment, the user can select one or more programs and/ortherapy schedules to submit to the memory 152 of the neuroregulator 104.For example, the user can cycle through available programs by repeatedlypressing the selection button 178 on the external charger 101. The usercan indicate the user's choice by, e.g., depressing the selector button178 for a predetermined period of time or pressing the selector button178 in quick succession within a predetermined period of time.

In use, in some embodiments, the external charger 101 may be configuredinto one of multiple modes of operation. Each mode of operation canenable the external charger 101 to perform different functions withdifferent limitations. In an embodiment, the external charger 101 can beconfigured into five modes of operation: an Operating Room mode; aProgramming mode; a Therapy Delivery mode; a Charging mode; and aDiagnostic mode.

When configured in the Operating Room mode, the external charger 101 canbe used to determine whether the implanted neuroregulator 104 and/or theimplanted lead arrangement 108 are functioning appropriately. If anycomponent of the therapy system 100 is not functioning as desired, thenthe medical personnel can trouble-shoot the problem while still in theoperation room or can abandon the procedure, if necessary.

For example, the external charger 101 can be used to determine whetherthe impedance at the electrodes 212, 212 a of the lead arrangement 108(FIG. 1) is within a prescribed range. When the impedance is within theprescribed range, a gastric contraction test can be initiated todemonstrate that the electrodes 212, 212 a are appropriately positionedand can become active. If the impedance is outside an acceptable range,the system integrity can be checked (e.g. connections to the leads canbe verified). Additionally, the therapy electrodes 212, 212 a may berepositioned to provide better electrode-tissue contact.

In another embodiment, the external charger 101 can be used to initiatea stomach contraction test in the operating room. The stomachcontraction test enables medical personnel to confirm the electrodes212, 212 a of the lead arrangement 108 (FIG. 1) are in contact with theappropriate nerves and not with some other tissue. For example, theexternal charger 101 can instruct the neuroregulator 104 to generate asignal tailored to cause the stomach to contract if the signal reachesthe appropriate nerves.

Typically, the external charger 101 is not connected to an externalcomputer 107 when configured in the Operating Room mode. In a preferredembodiment, the external charger is connected (e.g., via socket input176) to a physician coil 102′ (shown schematically in FIG. 6) instead ofa patient coil 102 (described above). The physician coil 102′ can differfrom the patient coil 102 in one or more respects.

For example, as shown in FIG. 6, a length L′ of the connection cable 102a′ on the physician coil 102′ can be longer than a length L of the cable102 a of the patient coil 102. In one example embodiment, the length L′of the connection cable 102 a′ of the physician coil 102′ can be about300 cm and the length L of the connection cable 102 a of the patientcoil 102 can be about 60 cm. The longer length L′ allows the externalcharger 101 to be located outside the sterile field in the operatingroom when the physician coil 102′ is connected.

In another embodiment, the physician coil 102′ can include an indicatorcircuit to identify the coil 102′ as a physician coil to the externalcharger 101. For example, the physician coil 102′ can contain a smallresistor 102 b′, which can be recognized by the external charger 101when the physician coil 102′ is plugged into the socket 176. When theexternal charger 101 detects the presence of the indicator circuit, theexternal charger 101 automatically configures itself into an OperatingRoom mode. This mode allows the physician to conduct various system andpatient response tests, such as those described above, without the needfor connection to a clinician computer 107.

When configured in the Programming mode, the external charger 101 isconnected with the external computer 107 (FIG. 1) via which thephysician manages the components of the therapy system 100. In general,the physician may select a therapy program and a therapy schedule storedon the external computer 107 to transfer to the external charger 101. Incertain embodiments, the external charger 101 forwards the programs andschedule to the neuroregulator 104. In an embodiment, the externalcharger 101 can be coupled to the physician coil 102′ duringprogramming. In another embodiment, the external charger 101 can becoupled to the patient coil 102. In addition, in different embodiments,the external computer 107 also can assess the impedance of theelectrodes 212, 212 a, initiate system and/or diagnostic tests, and takecorrective action when the external charger 101 is configured into theProgramming mode.

After the neuroregulator 104 has been implanted and the external charger101 and/or neuroregulator 104 have been programmed, the external charger101 can be configured into the Therapy Delivery mode. When configured inthe Therapy Delivery mode, the external charger 101 communicates withand/or powers the neuroregulator 104 as described above. Typically, theexternal charger 101 is coupled to the patient coil 102 and not to theexternal computer 107 when configured in the Therapy Delivery mode.

The external charger 101 also can interact with the user via the thirdinput (e.g., the selector button) 178 and the display 172 to select thetherapy to be provided. In an embodiment, the external charger 101 cansend instructions indicating which program the neuroregulator 104 shouldfollow while administering therapy. In another embodiment, the externalcharger 101 sends instructions in accordance with a selected programstored on the external charger 101.

If the neuroregulator 104 includes an internal power source 151, thenthe external charger 101 can enter a Charging mode in which the externalcharger 101 recharges the internal power source 151 of theneuroregulator 104 when the neuroregulator 104 is not deliveringtherapy. Typically, the external charger 101 enters the Charging mode atthe request of the neuroregulator 104. In a preferred embodiment, theneuroregulator 104 controls how much power is sent by the externalcharger 101.

During follow-up visits between the patient and the physician, theexternal charger 101 may be configured into a Diagnostic mode. In thismode, the external charger 101 is coupled to the external computer 107to provide an interface for the physician to obtain data stored on theexternal charger 101 and to download therapy and/or software updates. Inan embodiment, the display 172 on the external charger 101 is disabledand all information is conveyed to the physician via the externalcomputer 107 only. The external charger 101 may be coupled to eithercoil 102, 102′ when configured in the Diagnostic mode.

In an embodiment, the external charger 101 also can be configured into aShipping mode, in which the battery 182 is disconnected from the rest ofthe circuitry. The Shipping mode avoids draining the battery 182 andenhances safety. In one such embodiment, pressing the selector button172 causes the external charger 101 to change from this Shipping modeinto another mode, such as the Therapy Delivery mode.

c. Alignment of External and Implanted Coils

The external charger 101 enables alignment of the relative positions ofthe external and implanted coils 102, 105 and optimization of the signalstrength. Optimizing the alignment of the coils 102, 105 and the powerof the transmission signal facilitates continuous, transcutaneoustransmission of power and/or information.

i. Positioning of External Coil

In general, the external coil 102 is adapted to be placed on thepatient's skin (e.g., by adhesives) overlying the implanted internalcoil 105. The position and orientation of the coils 102, 105 can affectsignal reliability. In addition, the strength of the transmissionsignals between the external coil 102 and the implanted coil 105 also isaffected by the distance between the coils 102, 105. Implanting theneuroregulator 104 very close to the surface of the skin 103 typicallyresults in a large and expanded range of signal strengths. Conversely,implanting the neuroregulator 104 at a large distance beneath the skin103 yields a generally weak transmission link and a compressed range ofsignal strengths.

FIG. 7 illustrates an external coil 102 appropriately aligned with animplanted coil 105. The coil 105 is implanted beneath the skin 103 at apreferred depth D₁ (e.g., about two centimeters to about threecentimeters beneath the skin 103). Preferably, a plane of the coil 105extends parallel to the surface of the skin 103. In an embodiment, eachcoil 102, 105 is a circular coil surrounding a central axis X-X, Y-Y,respectively. As shown in FIG. 7, in a preferred alignmentconfiguration, the axes X-X, Y-Y are collinear so that there is nolateral offset of the axes X-X, Y-Y and the planes of the coils 102, 105are parallel to one another. Such an alignment configuration may beattained, e.g., when the external coil 102 is applied to a patient'sskin 103 when the patient is lying flat (e.g., on the patient's back).

FIG. 8 illustrates misalignment between the coils 102, 105 resultingfrom movement of the patient (e.g., a change in posture). For example,when the patient sits, excess fat may cause the skin 103 to roll. Thisrolling may cause the spacing between the coils 102, 105 to increase toa distance D2. Also, the orientation of the external coil 102 may changeso that the axes X-X and Y-Y of the coils 102, 105, respectively, have alateral offset T and an angular offset A. Such changes in spacing andorientation may be occurring constantly throughout the day.

The relative position of the coils 102, 105 may be optimized (e.g., foreach use) when the external charger 101 senses the transmission link isweakened (e.g., on initial power up or when the energy transfer to theimplantable neuroregulator 104 has degraded). For example, the externalcharger 101 can sound an alarm and invite the user to configure theexternal charger 101 into a Locate mode. Alternatively, the user candecide independently to enter the Locate mode (e.g., through a menuselection).

When configured in the Locate mode, the external charger 101 prompts theuser to adjust the orientation of the external coil 102 to achieve analignment (e.g., coaxial alignment) facilitating better coilinteraction. The external charger 101 also provides feedback to the userindicating the current degree of alignment of the coils 102, 105.Examples of such feedback include audio signals, lit LED's, bar graphsor other textual, graphical, and/or auditory signals provided to theuser.

In general, when the external charger 101 is configured in the Locatemode, the user sweeps the external coil 102 back and forth across thegeneral location of the implanted neuroregulator 104. During the sweep,the external charger 101 sends a locator signal S₁ to the implanted coil105 (see FIG. 7). The implanted coil 105 responds with a feedback signalS₂ (FIG. 7). The external charger 101 analyzes the feedback signal S₂ todetermine the strength of the transmission link between the coils 102,105.

In an embodiment, the external charger 101 keeps track of the strongestand weakest signals found during the sweep. The maximum signal strengthand the minimum signal strength can be indicated to the user, e.g., viathe visual display 172. These maximum and minimum values provide theuser with context for judging the relative strength of a given signal ateach location during the sweep. In an embodiment, the relative strengthof the signal at a given position also can be displayed to the user asthe user passes the external coil 102 over the position.

For example, in one embodiment, the first signal may be indicatedinitially as the maximum and minimum signal strength on the visualdisplay 172. As the external coil 102 is moved about, any subsequentsignals having greater signal strength replace the maximum signal shown.The strength of any subsequent, weaker signal also can be tracked by theexternal charger 101. The strength of the weakest signal can beindicated to the user as the minimum signal strength found. In oneembodiment, if the strength of a subsequent signal falls between thecurrently established values for minimum and maximum, then aninterpolated value representing the relative strength of the signal atthe respective coil position can be displayed.

Thus the external charger 101 learns the maximum and minimum values forsignal strength pertaining to external coil positions relative to thelocation of the implanted coil 105. By identifying the context of thesignal strength measurements (i.e., the maximum and minimum signalstrength found during a sweep), the external charger 101 can provideconsistent and context-sensitive measurements of signal strength to theuser regardless of the distance of the coil 102 from the implanted coil105. Such measurements facilitate identification of an optimum coilposition.

After the initial placement, the external coil 102 may need to berepositioned with respect to the implanted coil 105 to maintain thesignal integrity. The external charger 101 can monitor whether theneuroregulator 104 is receiving signals having sufficient signalstrength. If the external charger 101 determines the neuroregulator 104is not receiving a sufficient signal, then the external charger 101 maysound an alarm (e.g., auditory and/or visual) to alert the user thatcoil transmission effectiveness has been lost.

In an embodiment, after indicating the loss of transmissioneffectiveness, the external charger 101 may invite the user to configurethe external charger 101 into the Locate mode to reposition the externalcoil 102. Alternatively, the external charger 101 may invite the user tomodify the position of the external coil 102 without entering the Locatemode. In an embodiment, when the coil transmission effectiveness isre-established, the system automatically self-corrects and resumestherapy delivery.

ii. Dynamic Signal Power Adjustment

The amount of power received at the neuroregulator 104 can vary due torelative movement of the coils 102, 105 after the initial placement ofthe external coil 102. For example, the signal strength may vary basedon the distance between coils 102, 105, the lateral alignment of thecoils 102, 105, and/or the parallel alignment of the coils 102, 105. Ingeneral, the greater the distance between the coils 102, 105, the weakerthe transmission signal will be. In extreme cases, the strength of thetransmission signal may decrease sufficiently to inhibit the ability ofthe neuroregulator 104 to provide therapy.

The coils 102, 105 may move relative to one another when the patientmoves (e.g., walks, stretches, etc.) to perform everyday activities.Furthermore, even when the patient is inactive, the external coil 102may be placed on tissue with substantial underlying fat layers. Thesurface contour of such tissue can vary in response to changes inpatient posture (e.g., sitting, standing, or lying down). In thetreatment of obesity, the distance from the top layer of skin 103 to theimplanted coil 105 can vary from patient to patient. Moreover, thedistance can be expected to vary with time as the patient progresseswith anti-obesity therapy.

In addition, the power consumption needs of the neuroregulator 104 canchange over time due to differences in activity. For example, theneuroregulator 104 will require less power to transmit data to theexternal charger 101 or to generate therapy signals than it will need torecharge the internal battery 151.

To overcome these and other difficulties, an embodiment of the externalcharger 101 can change the amplification level of the transmissionsignal (e.g., of power and/or data) to facilitate effective transmissionat different distances between, and for different relative orientationsof, the coils 102, 105. If the level of power received from the externalcharger 101 varies, or if the power needs of the neuroregulator 104change, then the external charger 101 can adjust the power level of thetransmitted signal dynamically to meet the desired target level for theimplanted neuroregulator 104.

Adjustments to the power amplification level can be made either manuallyor automatically. In an embodiment, the external charger 101 maydetermine a target strength of the transmission signal (e.g., apredetermined strength selected to provide sufficient power to theneuroregulator 104), assess the effectiveness of the transmissionsignals currently being sent to the implanted coil 105, andautomatically adjust the amplification levels of the transmitted signalsto enhance the effectiveness of the transmissions between the externalcoil 102 and the implanted coil 105.

For example, if the neuroregulator 104 indicates it is recharging itsbattery 151, then the external charger 101 may establish a transmissionlink having a first power level appropriate for the task. At theconclusion of recharging, and when the neuroregulator 104 subsequentlyindicates it will begin therapy delivery, then the external charger 101may change the power of the transmission link to a second power levelsufficient to initiate therapy generation and delivery.

The external charger 101 also may increase the power level of the signalif the signal is lost due to separation and/or misalignment of thecoils. If the external charger 101 is unable to sufficiently increasethe power level of the transmitted signal, however, then the externalcharger 101 may issue an alarm and/or an invitation to the user toreposition the external coil 102 as described above.

The external charger 101 also may decrease the strength of the signal(i.e., the amount of power) being sent to the neuroregulator 104. Forexample, due to safety concerns, the amount of power that can betransmitted across skin via RF signals is limited. Receiving excessiveamounts of power could cause the neuroregulator 104 to heat up andpotentially burn the patient.

In an embodiment, the neuroregulator 104 includes a temperature sensor(not shown) configured to monitor the temperature of the neuroregulator104. The neuroregulator 104 can communicate the temperature to theexternal charger 101. Alternatively, the neuroregulator 104 can issue awarning to the external charger 101 if the neuroregulator 104 becomestoo warm. When the temperature of the neuroregulator 104 is too high,the external charger 101 may lower the power transmitted to theimplanted coil 105 of the neuroregulator 104 to bring the temperaturedown to an acceptable level. Alternatively, the neuroregulator 104 maydetune its receiving RF input circuit 157 to reduce power andtemperature.

In a preferred embodiment, the temperature of the neuroregulator 104should not exceed the surface temperature of the surrounding skin bygreater than about 2° C. (assuming a normal body temperature of 37° C.).Operational parameters, such as current, frequency, surface area, andduty cycle, also can be limited to ensure safe operation within thetemperature limit. Further details regarding safety concerns pertainingto transdermal power transmission can be found, e.g., in The CenelecEuropean Standard, EN 45502-1 (August 1997), page 18, paragraph 17.1,the disclosure of which is hereby incorporated by reference herein.

In an embodiment, the external charger 101 also can decrease the targetpower level based on a “split threshold” power delivery concept. In suchan embodiment, the external charger 101 initially provides a strongersignal than necessary to the neuroregulator 104 to ensure sufficientpower is available. The external charger 101 then reduces the strengthof the transmissions to a level just above the necessary signal strengthwhen the actual requirements have been established. This subsequentreduction in power saves drain on the external battery 182 or powersource 180.

For example, the external charger 101 can provide a low level of powercapable of sustaining basic operation of the neuroregulator 104 when theneuroregulator 104 indicates it is not actively providing therapy orrecharging its battery 151. When the neuroregulator 104 indicates it isabout to initiate therapy, however, the external charger 101 canincrease the power level of the transmission signal to a first thresholdlevel, which is comfortably in excess of the power required to providebasic operation of the neuroregulator 104 as well as provide therapy.When the actual power requirements for therapy delivery become apparent,the external charger 101 may decreases the power level of the signal toa second threshold level, which is closer to the minimum power levelrequired to provide basic functionality and maintain therapy delivery.

To perform this dynamic adjustment of signal strength, the externalcharger 101 analyzes a feedback signal (e.g., signal S₂ of FIG. 7)received from the implanted neuroregulator 104 indicating the amount ofpower required by the neuroregulator 104. The signal S₂ also may provideinformation to the external charger 101 indicating the power level ofthe signal S₁ being received by the implanted coil 105 of theneuroregulator 104. Such signal analysis would be within the skill ofone of ordinary skill in the art (having the benefit of the teachings ofthe present invention).

In an embodiment, the external charger 101 sets the signal power levelbased on a predetermined target power level for the transmission signalS₁. In response to the feedback signal S₂, the external charger 101modifies the power level of the transmission signal S₁ to be within atolerance range of the target power level. In an embodiment, theexternal charger 101 iteratively modifies the power level of thetransmission signal S₁ until the feedback signal S₂ indicates the powerlevel is within the tolerance range.

In addition to the dynamic adjustment of transmitted signal powerdescribed above, the neuroregulator 104 can be configured to optimizethe power received from the external charger 101 when the neuroregulator104 is recharging its battery 151. For example, the neuroregulator 104may tune (e.g., using a combination of hardware and software) thenatural resonant frequency of a recharging circuit (not shown) tomaximize the power delivered to a load resistance for a given set ofinput parameters such as voltage, current and impedance at the implantedcoil 105.

Transmission of power and/or information between the external charger101 and the implanted neuroregulator 104 is typically performed using acarrier frequency of 6.78 MHz. Emission requirements of industrial,scientific and medical equipment are governed by Federal CommunicationsCommission requirements described in FCC Title 47, Parts 15 and 18, andin EN 55011. The FCC requirements in the vicinity of this frequency aremore restrictive than those of EN 55011.

A preferred method for managing the temperature and carrier frequency ofthe neuroregulator 104 during the recharging process includes passing ahigh power unmodulated transmission between the external charger 101 andthe implantable neuroregulator 104 for a finite time (e.g., from abouthalf of a minute to about five minutes), during which time noinformational communication takes place between the external charger 101and the implantable neuroregulator 104 (i.e., no information is passedbetween the charger 101 and the neuroregulator 104). At the conclusionof this finite time period, the unmodulated transmission ceases.

An informational, modulated communicational transmission then is passedat low power (e.g., within the requirements of FCC Title 47 Part 15)during which the temperature of the implantable neuroregulator 104 iscommunicated periodically to the external charger 101. If thetemperature rises within certain restrictions (e.g., within therestrictions of The Cenelec European Standard, EN 45502-1 (August 1997),page 18, paragraph 17.1), then the communications transmission may beterminated, and the whole cycle may be repeated beginning with theinitiation of the high power, unmodulated, recharging transmission.

In an additional preferred embodiment, when the informational, modulatedcommunicational transmission is performed, the requisite signal power isreduced by using only externally transmitted power for the telemeteredcommunications, and by simultaneously using internal battery power tooperate the rest of the implanted circuitry 112 (FIGS. 3A and 3B), suchas a microcontroller and/or peripherals. In such embodiments, thetransmitted power may be less than if implant components(microcontroller and/or peripherals) also were receiving power from theRF transmission. Accordingly, the transmitted power may be limited tothe power required for communications at short distances of sixcentimeters or less. Advantageously, such a power reduction reduces thetotal power required to below FCC Part 15 limits for telemetrycommunications.

During the phase in which the battery 151 of the implantableneuromodulator 104 is being recharged by a high powered, unmodulatedtransmission (e.g., under the requirements of FCC Title 47 Part 18), thetemperature of the implanted neuroregulator 104 may be monitored and, ifnecessary, steps taken to inhibit the temperature from exceeding certainrequirements (e.g., the requirements of The Cenelec European Standard,EN 45502-1 (August 1997), page 18, paragraph 17.1). For example, thetemperature may be reduced by terminating the high powered, unmodulatedtransmission. In an alternative embodiment, the power level of the highpowered, unmodulated transmission may be reduced in later cycles tolimit the increase in temperature. In another embodiment, a control loopis established between the temperature rise and the power level of theunmodulated transmission to ensure the increase in temperature alwaysremains within the identified requirements.

d. Implanted Leads

FIG. 9 shows an example distal end of a bipolar lead, such as lead 106(see FIG. 1). The lead 106 includes a lead body 210 curved to receive anerve (e.g., a vagus nerve). The lead body 210 contains an exposed tipelectrode 212 configured to contact with the nerve received within thelead body 210. The tip electrode 212 is capable of delivering anelectrical charge to nerves having a diameter ranging from about onemillimeter to about four millimeters.

The lead body 210 also can have a suture tab 214 to attach the lead body210 to the patient's anatomy to stabilize the position of the lead body210. A first end of a flexible lead extension 216, which encloses aconductor from the electrode 212, couples with the lead body 210. Asecond, opposite end of the lead extension 216 terminates at a pinconnector (not shown) for attachment to a connector (e.g., an IS-1connector) 122 (shown in FIG. 1).

The lead 106 shown in FIG. 9 also includes a ring electrode 218surrounding the lead extension 216 at a position spaced from the tipelectrode 212. In an embodiment, the surface area of each electrode 212,218 is greater than or equal to about thirteen square millimeters. Asuture tab 220 may be provided for placement of the ring electrode 218on the patient's anatomy in general proximity to the placement of thetip electrode 212 on the nerve.

In an alternative embodiment, a monopolar lead (not shown) may beimplanted instead of the bipolar lead 106. Typically, the monopolar leadis the same as the bipolar lead 106, except the monopolar lead lacks aring electrode 218. Such a monopolar lead is described in commonlyassigned and co-pending U.S. patent application Ser. No. 11/205,962, toFoster et al, filed Aug. 17, 2005, the disclosure of which is herebyincorporated by reference.

Further details pertaining to example electrode placement andapplication of treatment can be found, e.g., in U.S. Pat. No. 4,979,511to Terry, Jr., issued Dec. 25, 1990; U.S. Pat. No. 5,215,089 to Baker,Jr., issued Jun. 1, 1993; U.S. Pat. No. 5,251,634 to Weinberg, issuedOct. 12, 1993; U.S. Pat. No. 5,531,778 to Maschino et al., issued Jul.2, 1996; and U.S. Pat. No. 6,600,956 to Maschino et al., issued Jul. 29,2003, the disclosures of which are hereby incorporated by referenceherein.

2. Placement of Electrodes and Electrode Configuration Options

FIG. 10 shows a posterior vagus nerve PVN and an anterior vagus nerveAVN extending along a length of a patient's esophagus E. The posteriornerve PVN and the anterior AVN are generally on diametrically oppositesides of the esophagus E just below the patient's diaphragm (not shown).A first tip electrode 212 of a lead arrangement 108 (FIG. 1) is placedon the anterior vagus nerve AVN. A second electrode 212 a of the leadarrangement 108 is placed on the posterior vagus nerve PVN. Theelectrodes 212, 212 a are connected by leads 106, 106 a to aneuroregulator 104 (FIG. 1).

At the time of placement of the leads 106, 106 a, it may be advantageousfor the tip electrodes 212, 212 a to be individually energized with astimulation signal selected to impart a neural impulse to cause adetectable physiological response (e.g., the generation of antropyloricwaves). The absence of a physiological response may indicate the absenceof an overlying relation of the tested electrode 212, 212 a to a vagusnerve PVN, AVN. Conversely, the presence of a physiological response mayindicate an overlying relation (e.g., correct placement) of the testedelectrode 212, 212 a to a vagus nerve. After determining the leads 106,106 a create a physiologic response, the electrodes 212, 212 a can beattached to the nerves PVN, AVN.

A preferred embodiment of the leads 106, 106 a for treating obesity isshown in FIG. 10. The lead arrangement 108 includes bipolar leads 106,106 a. The bipolar leads 106, 106 a each include one tip (i.e., orcathode) electrode 212, 212 a that can be placed directly on the nervePVN, AVN and one ring (i.e., or anode) electrode 218, 218 a that is notplaced on the nerve PVN, AVN, but rather may be attached to anotherstructure (e.g., the stomach). In other embodiments, however, the leadarrangement 108 may include monopolar leads (i.e., each lead 106, 106 ahaving only a tip electrode 212, 212 a).

Electrical connection between the neuroregulator 104 and the therapyleads 106, 106 a is made through bipolar IS-1 compatible lead adapters122, 122 a attached to the neuroregulator 104. If the bipolar leaddesign is used, two bipolar electrode pairs—one for the anterior vagusand one for the posterior vagus—are provided. One bipolar lead feeds abipolar electrode pair. If the monopolar lead design is used, only theconductor connected to the distal tip electrode of each bipolar IS-1connector is used.

The therapies as previously described could be employed by usingblocking electrodes or stimulation electrodes or both in order todown-regulate and/or up-regulate the vagus nerve. A blocking signaldown-regulates a level of vagal activity and simulates, at leastpartially, a reversible vagotomy.

Referring to FIGS. 11-18, the pacing signals to the electrodes 212, 212a can be selected to create different types of signals and signal paths(referred to herein as “configurations”). FIGS. 11-18 illustrate fourdifferent electrode configurations.

a. Blocking Electrode Configuration (1)

A first blocking electrode configuration is shown in FIG. 11. Thisconfiguration creates a current path (see arrow 1 in FIG. 11) withcurrent flowing between the anterior and posterior nerves AVN, PVN. Thetip electrodes 212, 212 a, which are located directly on the anteriorand posterior vagal nerves AVN, PVN, respectively, are electricallyactive. The anodic ring electrodes 218, 218 a are not energized.

A continuous waveform (e.g., the square waveform W₁₀ shown in FIG. 12)propagates along the current path (see arrow 1) extending across theesophagus E. Such an electrode configuration is generally monopolar(i.e., only one location on each nerve PVN, AVN is subject to thetreatment) and could be accomplished with monopolar leads (i.e., leadswithout ring electrodes 218, 218 a).

b. Blocking Electrode configuration (2)

FIG. 13 illustrates a second blocking electrode configuration in whicheach of the tip electrodes 212, 212 a is associated with an anodeelectrode 218, 218 a, respectively. Therapy signals are applied only tothe anterior vagus nerve AVN between the distal electrode 212 and theanode electrode 218. Advantageously, current (see arrow 2 in FIG. 13)does not flow through the esophagus E, thereby decreasing the likelihoodof the patient sensing the treatment (e.g., feeling discomfort or pain).

In general, the anode electrodes 218, 218 a can be positioned on anyanatomical structure. In a preferred embodiment, the anode electrodes218, 218 a are placed on structures in generally close proximity (e.g.,within about five centimeters) of the tip electrodes 212, 212 a. Forexample, the anode electrodes 218, 218 a can be placed on the same vagalnerve PVN, AVN as the anode electrode's associated electrode 212, 212 a.

In other embodiments, however, the anode electrodes 218, 218 a can beplaced on the stomach, the esophagus, or other anatomical structure inthe general vicinity of the electrodes 212, 212 a. In an embodiment, theanode electrodes 218, 218 a can be placed on the stomach to permitmonitoring of stomach contractions (e.g., by strain receptors associatedwith the anode electrodes 218, 218 a). The arrangement of FIG. 13results in a pacing waveform W₁₁ (FIG. 14).

c. Blocking Electrode Configuration (3)

FIG. 15 illustrates the same electrode configuration shown in FIG. 13,except the signals are applied only to the posterior vagus nerve PVNbetween the tip electrode 212 a and the anode electrode 218 a. Thecorresponding current path is shown by arrow 3 in FIG. 15. In anembodiment, the example signal waveform W₁₂ (see FIG. 16) propagatingacross the current path is the same as the waveform W₁₁ in FIG. 14. Inother embodiments, however, any desired waveform can be utilized.

d. Blocking Electrode Configuration (4)

The electrode configuration of FIG. 17 is generally the same as theelectrode configurations of FIGS. 11, 13 and 15. In FIG. 17, however, anelectrically active anode (e.g., ring electrode 218, 218 a) and cathode(e.g., tip electrode 212, 212 a) are associated with each nerve PVN, AVNto provide a dual channel system. Such an electrode arrangement routescurrent flow through both nerves PVN, AVN as indicated by arrows 4.

In an embodiment, a first electrode (e.g., the tip electrode 212, 212 a)is placed directly on each of the nerve trunks and a second electrode(e.g., ring electrode 218, 218 a) is located in proximity to the firstelectrode. Two waveforms (e.g., an anterior nerve waveform W_(12A) and aposterior nerve waveform W_(12P) shown in FIG. 18) are generated. In theexample shown, the pulses of one of the waveforms occur during no-pulseperiods of the other waveform. In such a configuration, a completecharging and rebalancing cycle can occur on one channel before thesecond channel is charged and rebalanced. Accordingly, only one channelis electrically paced at a time. Typically, the electrodes on the nerveare energized cathodically first.

3. Post-Operative Testing of Electrodes

After completing implantation, assembly, and positioning of theneuroregulator 104 and the electrode arrangement 108, a physician candetermine the lead integrity by measuring the lead impedance andassessing whether the lead impedance is within an acceptable range. Ifthe lead impedance is within range, the physician can connect anexternal computer 107 (e.g., a clinician computer) to the externalcharger 101 (see FIG. 1).

The clinician computer 107 can transmit treatment therapy settings andtreatment data to the neuroregulator 104 via the external charger 101.The clinician computer 107 also can retrieve data from the externalcharger 101 or neuroregulator 104. For example, in one embodiment, theclinician computer 107 detects serial numbers of the external charger101 and neuroregulator 104 automatically. After adjustment of blockingparameters and retrieval of data, the clinician computer 107 may bedisconnected from the external charger 101.

After the patient has adequately recovered from the surgery (e.g.,approximately fourteen days after the implantation surgery), thephysician may program initial treatment parameters into the externalcharger 101. For example, the physician can couple the cliniciancomputer 107 to the external charger 101 and follow menu commands on thecomputer 107 to upload select therapy programs to the external charger101. In certain embodiments, the uploaded programs can then betransferred to the implanted neuroregulator 104.

Additionally, the physician can use the clinician computer 107 to selecttreatment start times for the patient. In an embodiment, treatment starttimes are selected based on the individual patient's anticipated wakingand initial meal times. The start times can be set differently for eachday of the week. Further details regarding scheduling treatment will bediscussed herein with respect to FIG. 19.

4. System Software

The external charger 101 and the neuroregulator 104 contain software topermit use of the therapy system 100 in a variety of treatmentschedules, operational modes, system monitoring and interfaces as willbe described herein.

a. Treatment Schedule

To initiate the treatment regimen, the clinician downloads a treatmentspecification and a therapy schedule from an external computer 107 tothe external charger 101. In general, the treatment specificationindicates configuration values for the neuroregulator 104. For example,in the case of vagal nerve treatment for obesity, the treatmentspecification may define the amplitude, frequency, and pulse width forthe electrical signals emitted by the implanted neuroregulator 104. Inanother embodiment, “ramp up” time (i.e., the time period during whichthe electrical signals builds up to a target amplitude) and “ramp down”time (i.e., the time period during which the signals decrease from thetarget amplitude to about zero) can be specified.

In general, the therapy schedule indicates an episode start time and anepisode duration for at least one day of the week. An episode refers tothe administration of therapy over a discrete period of time.Preferably, the clinician programs an episode start time and durationfor each day of the week. In an embodiment, multiple episodes can bescheduled within a single day. Therapy also can be withheld for one ormore days at the determination of the clinician.

During a therapy episode, the neuroregulator 104 completes one or moretreatment cycles in which the neuroregulator 104 sequences between an“on” state and an “off” state. For the purposes of this disclosure, atreatment cycle includes a time period during which the neuroregulator104 continuously emits treatment (i.e., the “on” state) and a timeperiod during which the neuroregulator 104 does not emit treatment(i.e., the “off” state). Typically, each therapy episode includesmultiple treatment cycles. The clinician can program the duration ofeach treatment cycle (e.g., via the clinician computer 107).

When configured in the “on” state, the neuroregulator 104 continuouslyapplies treatment (e.g., emits an electrical signal). The neuroregulator104 is cycled to an “off” state, in which no signal is emitted by theneuroregulator 104, at intermittent periods to mitigate the chances oftriggering a compensatory mechanism by the body. For example, if acontinuous signal is applied to a patient's nerve for a sufficientduration, the patient's digestive system eventually can learn to operateautonomously.

An example daily treatment schedule 1900 is schematically shown in FIG.19. The daily schedule 1900 includes a timeline indicating the timesduring the day when the treatment is scheduled to be applied to apatient. Duty cycle lines (dashed lines) extend along the time periodsduring which treatment is scheduled. For example, a first episode isscheduled between 8 AM and 9 AM. In certain embodiments, the treatmentschedules 1900 address other details as well. For example, the dailyschedule 1900 of FIG. 19 indicates details of the waveform (e.g.,ramp-up/ramp-down characteristics) and details of the treatment cycles.

b. System Operational Modes

The therapy system 100 can be configured into two basic operationalmodes—a training mode and a treatment mode—as will be described herein.In an embodiment, the therapy system 100 also can be configured into aplacebo mode for use in clinical trials.

i. Training Mode

The training mode is used post-operatively to train the patient on usingthe therapy system 100. In this mode, electrical signals are notdelivered to the nerves for the purpose of creating blocking actionpotentials. In a preferred embodiment, the neuroregulator 104 does notgenerate any electrical signals. In some embodiments, the trainingtherapy setting can be preset by the therapy system manufacturer and areunavailable to the treating physician.

The training mode allows the physician to familiarize the patient withthe positioning of the external charger 101 relative to the implantedneuroregulator 104. The physician also instructs the patient in how torespond to the feedback parameters within the therapy system 100.Training also can cover information and menus which can be displayed onthe external charger 101, for example: the status of the battery 182 ofthe external charger 101, the status of the battery 151 of the implantedneuroregulator 104, coil position, lead/tissue impedances, and errorconditions.

The physician also can train the patient in how to interact with theexternal charger 101. In an embodiment, the patient interacts with theexternal charger 101 using the selection input button 174. For example,by successively pressing the button 174, the patient can select one ofmultiple device operations, such as: device reset, selectiveinterrogation of battery status, and coil position status.

ii. Treatment Mode

The treatment mode is the normal operating mode of the neuroregulator104 in which the neuroregulator 104 applies a blocking signal to thenerves using blocking therapy settings. In general, the therapy settingsare specified by the physician based on the specific needs of thepatient and timing of the patient's meals. In some embodiments, theneuroregulator 104 controls the therapy being provided according totherapy programs and schedules stored on the neuroregulator 104. Inother embodiments, the neuroregulator 104 follows the instructions ofthe external charger 101 to deliver therapy.

iii. Placebo Mode

This mode may be used for patients randomized to a placebo treatment ina randomized, double-blind clinical trial. In this mode, theneuroregulator 104 does not apply therapy signals to the leadarrangement 108. Rather, in different embodiments, therapy signals canbe supplied to a dummy resistor to drain the internal power source 151(FIG. 3) of the neuroregulator 104.

The external charger 101 interacts with the patient and the physician asif therapy was being applied. For example, the patient and/or physiciancan view system status messages and a battery drain rate of the externalcharger 101 and neuroregulator 104. Because the external charger 101functions as normal, the physician and the patient are blind to the factthat no significant therapy is being applied.

To give the patient the sensation that therapy is being applied, currentpulses may be applied to the vagal nerve trunks during impedancemeasurements at the start of therapy. However, no therapy is deliveredduring the remainder of the blocking cycle. These sensations are felt bythe patient and provide a misleading indication of activity. Thesesensations, therefore, help in maintaining the double blindness of thestudy.

c. Treatment Therapy Settings

The neuroregulator 104 is configured to provide therapy signals to theelectrode arrangement 108. In general, the therapy signals can inducestimulation of the nerves, blocking of nerve impulses, or somecombination of the two.

i. Blocking Treatment

During treatment, the neuroregulator 104 provides blocking signals tothe nerves of a patient. Blocking signals include high frequencywaveforms that inhibit the transmission of signals along the nerves. Ingeneral, the physician selects and sets therapy settings (e.g., waveformcharacteristics and treatment schedule) based on meal times and apatient's eating pattern. In an embodiment, the therapy system 100 canprovide a choice of at least three unique blocking therapy settingswhich can be applied as part of a daily treatment schedule.

ii. Low Frequency Mode

The low frequency mode provides low frequency stimulating signals alongthe patient's nerves to create a brief, potentially observable,physiological response as an intra-operative screen. Such a physiologicresponse could be, for example, the twitching of a muscle or organ, suchas the stomach.

This therapy setting may be used by the physician to confirm correctelectrode placement. The system operates in this mode for short timeperiods and, typically, only when the patient is under physician care.This mode may be accessed through the programmer interface. In anembodiment, this mode can be enabled/disabled (e.g., by themanufacturer) through the programming interface.

iii. Temporary Test Therapy Setting Mode

The therapy system 100 has the ability to program specialtreatment/testing therapy settings to support “one-time” physiologicalevaluations. Special testing therapy parameters can be preset (e.g., bythe manufacturer) to be made available for use by the physician.

d. System Monitoring

The therapy system 100 facilitates monitoring the operation of thetherapy system 100 and its components. By monitoring the operation ofthe therapy system 100, faults and malfunctions can be caught early anddealt with before becoming problematic. The therapy system 100 canrecord the operation and/or the fault conditions for later analysis. Thetherapy system 100 also can notify the patient and/or physician of thesystem operating status and non-compliant conditions. For example, anerror message can be displayed on screen 172 (see FIG. 5) of theexternal charger 101 or on a display screen (not shown) of the externalcomputing device 107 (see FIG. 1).

Embodiments of the therapy system 100 can confirm proper functioning ofand communication between the components of the therapy system 100. Forexample, the therapy system 100 can monitor the link strength betweenthe external charger 101 and the neuroregulator 104. In an embodiment,immediate feedback indicating the link strength can be provided to thepatient (e.g., through the display 172 of the external charger 101)and/or to the physician (e.g., through the external computing device107).

The therapy system 100 also can determine one or both of the coils 102,105 are broken, shorted, or disconnected. In an embodiment, the therapysystem 100 determines whether the coils 102, 105 are operational bymeasuring the impedance between the coils and determining whether themeasured impedance falls within an acceptable range.

The therapy system 100 also can measure the impedance between theelectrodes 212, 212 a of the lead arrangement 108 and determine whetherthe impedance is out of range (e.g., due to inadequate electrode-nervecontact, or shorted electrodes). Details regarding the measurement oflead impedance are discussed later herein. Impedance measurements alsocan be used to verify proper lead placement, verify nerve capture, andmonitor stomach contraction during the implant procedure.

The therapy system 100 also can communicate other types of systemerrors, component failures, and software malfunctions to the patientand/or physician. For example, the therapy system 100 can monitor thebattery status (e.g., low battery, no charge, battery disconnected,etc.) of the neuroregulator 104 and/or the external charger 101 and warnthe patient and/or physician when the battery should be recharged and/orreplaced.

The therapy system 100 can indicate an inability to deliver a signalhaving the specified current (e.g., due to the impedance being out ofrange or due to internal component failure) to the lead arrangement 108during treatment delivery. The therapy system 100 also can indicatewhether the external charger 101 and/or the neuroregulator 104 havesufficient power to transmit and/or receive signals (e.g., based onantenna alignment, battery power, etc.).

i. Lead Impedance Measurement

Embodiments of the therapy system 100 have the ability to independentlymeasure and record lead impedance values. Lead impedance values outsidea predefined range may indicate problems or malfunctions within thetherapy system 100. High impedance, for example, could mean that theelectrodes 212, 212 a are not properly coupled to the nerves of thepatient. Low impedance could mean inappropriate shorting of theelectrodes 212, 212 a.

These embodiments of the therapy system 100 allow the physician tomeasure lead impedance on-demand. The therapy system 100 also canenables the physician to periodically measure impedance (e.g., duringthe Training Mode) without initiating a blocking therapy setting.Generally, impedance is measured and stored separately for each channelof each electrode configuration. These measurements may be used toestablish a nominal impedance value for each patient by calculating amoving average. The nominal impedance and impedance tolerance range canbe used for system non-compliance monitoring, as will be describedbelow.

e. External Computer Interface

Programmer software, with which the physician can program treatmentconfigurations and schedules, resides on and is compatible with anexternal computing device 107 (FIG. 1) that communicates with theexternal charger 101. In general, application software for the computingdevice 107 is capable of generating treatment programs stored in acommonly accepted data file format upon demand.

The programming interface of the computing device 107 is designed toenable the physician to interact with the components of the therapysystem 100. For example, the programming interface can enable thephysician to modify the operational modes (e.g., training mode,treatment mode) of the external charger 101. The programming interfacealso can facilitate downloading treatment parameters to the externalcharger 101. The programming interface enables the physician to alterthe treatment parameters of the neuroregulator 104, and to scheduletreatment episodes via the external charger 101.

The programming interface also enables the physician to conductintra-operative testing amongst the components of the therapy system100. For example, the physician can initiate a lead impedance test viathe programming interface. The physician also can program temporarytreatment settings for special physiologic testing. The programminginterface also can facilitate conducting diagnostic stimulation atfollow-up visits between the patient and the physician.

The programming interface of the computing device 107 also enables thephysician to access patient data (e.g., treatments delivered and notedphysiological effects of the treatment). For example, the programminginterface can enable the physician to access and analyze patient datarecorded by the therapy system 100 (e.g., stored in the memory 152 ofthe neuroregulator 104 and/or the memory 181 of the external charger101). The physician also can upload the patient data to the externalcomputing device 107 for storage and analysis.

The programming interface also can enable the physician to view systemoperation information such as non-compliant conditions, system faults,and other operational information (e.g., lead impedance) of the therapysystem 100. This operational data also can be uploaded to the externalcomputing device 107 for storage and analysis.

i. Programming Access Level

In certain embodiments, the programming interface defines at least twolevels of access, one for the physician and one for the systemmanufacturer. The programming interface can provide different types ofinformation to a requestor depending on what level of access therequestor has. For example, the programming interface may enable thesystem manufacturer to program system settings (e.g., default values fortreatment parameters, acceptable ranges for treatment parameters and/orsystem settings, system tolerances, etc.) that cannot be adjusted by thephysician.

In an embodiment, a user with a high level of access can select, foreach system setting, the level of access required before the programminginterface will enable a user to modify the system setting. For example,the system manufacturer may wish to prevent treating physicians frommodifying default treatment settings. It will be appreciated thatgenerating software implementing the above-described features of theprogramming interface is within the skill of one of ordinary skill inthe art having the benefits of the teachings of the present application.

5. Charge Balancing

Nerves may be damaged when exposed to direct current (e.g., net currentfrom electrical stimulation) over extended periods of time. Such damagemay result from very small net currents acting over a long time, e.g.microamperes of current over minutes. For example, direct current can becaused by a voltage buildup at the electrodes 212, 212 a (FIG. 1) due toinherent differences in electrode component values.

Charge-balancing advantageously mitigates (and may eliminate) damage tothe nerve due to charge build-up during treatment. However, conventionalprocesses for achieving a current/charge balance to within (for example)1 μA in a current of about 6 mA place inordinate requirements on theimplantable device of providing consistent power at a consistentfrequency. Below are descriptions of two processes for balancing charge,a timing process and a shorting process, that do not require suchinordinate consistency.

a. Timing Correction

Referring to FIGS. 20-24, charge or current on the patient's nerves canbe balanced by applying a correction to a pulse-width PW of a treatmentsignal pulse 2000 over a number of cycles (see FIG. 20). A cycle refersto a single iteration of the pulse. The correction includes adding orsubtracting a “timer tick” to the pulse-width PW of at least one phaseof the treatment signal pulse 2000 to increase or decrease thepulse-width for a period of time. In an embodiment, an example timertick can equate to the minimum resolution of the applied clock frequency(e.g., about 560 nanoseconds).

Typically, the treatment signal pulse 2000 is a bi-phasic (e.g., havinga negative phase and a positive phase) pulse signal having a pulse-widthPW. In general, the negative charge provided by the first phase of thesignal pulse 2000 is balanced by the positive charge provided by thesecond phase of the signal pulse 2000. One or more timer ticks can beadded to one or both phases of the pulse 2000 to correct a chargeimbalance.

In the example shown in FIG. 20, the first phase of the signal pulse2000 has a first pulse-width PW1 and the second phase of the signalpulse 2000 has a second pulse-width PW2. One or more timer ticks can beadded to the pulse-width PW1, PW2 of one or both phases of the signalpulse 2000. For example, the pulse-width PW1 of the first phase can beincreased by two timer ticks to a pulse-width of PW1′. Alternatively,the pulse-width PW2 of the second phase can be decreased by two timertick to a pulse-width of PW2′.

To determine the number of timer ticks to add or subtract from eachpulse-width, the neuroregulator 104 periodically can measure the voltageof the signal applied to each lead electrode 212, 212 a of leadarrangement 108. The combination of charge buildup sensing and pulsewidth control creates a feedback loop to minimize the resulting voltageoffset. Advantageously, this sense and control process is effective inthe presence of physiologic variations, circuit tolerances, differencesin electrode size, and temperature changes.

For example, as shown in FIGS. 3A and 3B, the electrodes of each lead(e.g., the tip electrodes 212, 212 a in contact with the anterior andposterior vagal nerves AVN, PVN, respectively) are coupled to the CPU154 of the neuroregulator 104 via a capacitive divider 162. The CPU 154provides timed instructions to the output module 161 for controlling thevoltage measurements VA, VB of the signals applied by the electrodes212, 212 a (FIG. 1).

Between pulses, the microprocessor CPU 154 can zero the capacitivedivider 162, release the capacitive divider 162 at a predetermined timerelative to the signal cycle, and measure the voltages VA, VB of theelectrodes 212, 212 a. For example, the CPU 154 can zero the capacitivedivider 162, release the capacitive divider 162 approximately tenmicroseconds into a negative phase of the pulse, and measure thevoltages VA, VB (see FIG. 20). The CPU 154 can subsequently measure thevoltages VA, VB at approximately 10 microseconds into a positive phaseof the pulse. If the voltage measurement VA of the electrode 212 isgreater than the voltage measurement VB of the second electrode 212 a,then the CPU 154 delivers instructions to decrease the pulse width(e.g., by about 560 nanoseconds) of the negative phase of the pulse ofthe next/subsequent cycle.

The above process may be repeated at a sampling frequency (e.g.,typically about 40 Hz). Gradually, the number of pulse width correctiveincrements (“timer ticks”) applied to the signal can be adjusted. Forexample, the pulse width PW1 of the positive phase of the pulse can beincreased or decreased every sample period until the voltage measurementVA of the first electrode 212 is less than the voltage measurement VB ofthe second electrode 212 a. In such a case, the pulse width PW2 of thenegative pulse then can be increased to achieve balance. When themaximum pulse width PW2 of the negative phase of the pulse is reached,then the pulse width PW1 of the positive phase of the biphasic pulse maybe decreased to maintain balance. In a preferred embodiment, thecorrective increment is applied to a series of signals until the netoffset current is well below a target current (e.g., about 1 μA).

In an embodiment, the amplitudes of the positive and negative phases ofthe pulse are compared very early in the cycle, and a relatively largecorrection is initially applied to the pulse width of the signal.Subsequently, the balancing correction is refined by changing the pulsewidth by only the one or two ticks as described above.

Advantageously, the charge-balancing goal can be achieved over a numberof these cycles using the above described processes without requiring ahigh clock frequency. Because the charge buildup tends to be a slowprocess, correcting the charge buildup can be done less frequently thandelivering therapy signals. For example, in an embodiment, therapysignals can be delivered at about 5 kHz and correction pulses can bedelivered at about 40 Hertz.

FIG. 21 illustrates an example application of charge balancing throughtiming corrections. FIG. 21 illustrates a blocking waveform 222 (e.g., abiphasic, symmetric current waveform), which results in a voltagewaveform 224 at the electrode-tissue interface. The voltage waveform 224includes an exponential voltage component 226 which reflects the factthat the electrode-tissue interface has capacitive elements, resultingin charging and discharging of this capacitance.

In one cycle of the current waveform 222, the charge applied to theelectrode-tissue interface is balanced when the voltages V_(C) and V_(D)are equal. Accordingly, in such a case, the net potential of theelectrode-tissue interface is zero. As described above, however, thereare a number of reasons why, in practice, voltages V_(C) and V_(D) maynot be equal, resulting in a charge imbalance.

Typically, in practical operation, the voltage values of V_(C) and V_(D)are measured periodically (e.g., about every 25 milliseconds). If thevoltage V_(C) is greater than the voltage V_(D), then the pulse width228 of the first phase of the current waveform 222 is reduced by one“timer tick,” and applied for about 1 millisecond. At the end ofsubsequent measurement periods (e.g., about every 25 milliseconds), thevalues of voltages V_(C) and V_(D) are measured again. When the voltageV_(C) is greater than the voltage V_(D), the pulse width 228 of thefirst phase is reduced by an additional timer tick. The current waveform222 having the phase with the reduced pulse-width 228 is applied for anadditional 1 millisecond.

When the value of the voltage V_(C) is eventually less than the value ofthe voltage V_(D), then the pulse width 228 of the first phase can beincreased by one timer tick for 1 millisecond for each measurementperiod. In this situation, it may be that the maximum pulse width (asdetermined by the applied frequency of the therapy) 228, is reachedwhile the voltage V_(C) is still less than the voltage V_(D). If thisoccurs, then the pulse width 230 of the second phase of the currentpulse 222 is decreased one timer tick at a time, as described above,until equilibrium is established (i.e., V_(C)=V_(D)).

Additionally, in the methods represented by FIGS. 20 and 21, themicroprocessor CPU 154 can short out the electrodes 212, 212 a at thebeginning, midpoint and/or end of the biphasic, square-wave, currentpulse, as described in more detail herein. Over a series of suchsampling cycles, it has been demonstrated that the net offset current iswell below the design goal of 1 μA.

During a feedback cycle, software stored in the microprocessor CPU 154can initiate a therapy shut down if the sensed voltage offset exceedssafe values. This is an advantageous feature in actual use, whereelectrode configurations and other parameters could vary.

By using a combination of both hardware (i.e., electrode shorting) andclosed-loop software techniques, the average charge imbalance may belower than with either method individually.

At the end of therapy delivery, it is useful to have the hardwarebriefly drain any residual charge. Subsequently, the circuitry may bemade safe until the next therapy delivery and the software loop turnedoff.

b. Shorting Correction

Some processing for achieving charge balance have involved the use ofbiphasic pulses in which, for example, the negative charge provided bythe first part of the waveform is balanced by the positive chargeprovided by the second part of the waveform. Further details describingthe use of electrode shorting to achieve charge balancing can be foundin U.S. Pat. No. 4,498,478 to Bourgeois, issued Feb. 12, 1985; U.S. Pat.No. 4,592,359 to Galbraith, issued Jun. 3, 1986; and U.S. Pat. No.5,755,747 to Daly et al, issued May 26, 1998, the disclosures of whichare hereby incorporated by reference herein.

FIGS. 22-24 illustrate a preferred charge balancing process. FIGS. 22and 23 schematically illustrate an implanted circuit 112 of aneuroregulator 104 connected to nerve electrodes 212, 212 a. The circuit112 has components schematically illustrated as a switch 150 forselectively creating an electrical short between the electrodes 212, 212a. In FIG. 22, the switch 150 is arranged in a short state to create anelectrical short between electrodes 212, 212 a. In FIG. 23, the switch150 is arranged in a non-short state with no short being created betweenthe electrodes 212, 212 a.

FIG. 24 schematically illustrates signal waveforms W₁, W₂, W_(1A),W_(2A) produced at the electrodes 212, 212 a under various conditions ofoperation of the switch 150. The waveforms W₁ and W₂ show the signalsproduced at electrodes 212, 212 a, respectively, when the switch 150 isarranged in the non-short state. Each waveform W₁ and W₂ has a negativepulse and a positive pulse of equal pulse width PW. The waveforms W₁, W₂are out of phase so that the negative pulses of the waveform W₁ occurduring the positive pulses of the waveform W₂.

It will be appreciated, these waveforms are illustrative only. Any otherwaveform (e.g., the time offset waveform W_(12A) of FIG. 18 could beused). In addition, while the short is shown between electrodes 212, 212a, the short alternatively or additionally could be created betweencathode and anode pairs 212, 218 and 212 a, 218 a, previously described.

In the example shown, the switch 150 is operated to create a shortbetween electrodes 212, 212 a at the start of each pulse and for aduration Ds. The waveforms at electrodes 212, 212 a resulting from suchshorting are shown in FIG. 24 as W_(1A), W_(2A). As a result of theshort, any charge build-up at an electrode (e.g., electrode 212) isdistributed to the oppositely charged electrode (e.g., electrode 212 a).The pulse width PW of each pulse is reduced to a pulse width PW_(A).Advantageously, repeating this process throughout the therapy maintainsany net charge build-up below tolerable levels.

The example given shows the short state occurring at the beginning ofeach signal pulse. This is illustrative only. The short state can occurat the beginning, end or any intermediate time of a signal pulse.Furthermore, the short state need not be applied to every pulse, butrather can occur intermittently throughout the pulse cycles or evenduring time delays between pulses. When applied during a pulse cycle,the duration Ds of the short is preferable not greater than about 10% ofthe pulse width PW. For example, the duration Ds can range from about 10μs to about 20 μs.

6. Therapy Calibration and Safety Limits

The design of the neuroregulator 104 (FIG. 3) includes a capacitivedivider 162 and an output module 161 to measure the voltage present atthe lead arrangement 108 (e.g., the tip electrodes 212, 212 a and/orring electrodes 218 and 218 a of both anterior and posterior leads 106,106 a). The output module 161 can measure the current flow through theelectrodes arranged in any of the four electrode configurations (seeFIGS. 11, 13, 15, and 17). A programmable current source (not shown) canenable a physician to select how current is delivered through theelectrodes 212, 212 a, 218, and 218 a to the nerve.

Before therapy is delivered, the physician can calibrate theneuroregulator 104 to ensure the desired current can be delivered to thenerves. For example, this calibration can be accomplished by connectingthe programmable current source from a power source to ground andadjusting the current to the desired level. Current does not flowthrough the leads 106 during this calibration procedure. If the desiredcurrent cannot be delivered, or if the DC voltage offset is greater thana programmed limit, then the therapy can be terminated (e.g., suchconditions trigger a flag or error alert).

Advantageously, calibrating the therapy system 100 significantly reducesthe effect of component tolerance, drift, and aging on the amount ofcurrent delivered. Temperature effects are not likely to be significantsince the neuroregulator 104 is at body temperature when implanted. Inaddition, the capacitive divider 162 can be calibrated before therapy isdelivered. Advantageously, calibrating the divider 162 can enhance theaccuracy of the safety checks from a 20% worst case value toapproximately 2%.

During therapy, the current between the active electrodes is measuredduring each signal pulse to ensure that the delivered current is withinthe programmed tolerance (e.g., +/−about 5%).

Additionally, in order to determine the state of charge balance, thetherapy system 100 can determine a peak-to-peak voltage quantity foreach signal pulse. The peak-to-peak voltage quantity is divided by twoand compared to the peak voltage measurement of each phase of thewaveform. If the deviation exceeds a predetermined value, the therapycan be shut down.

The normal shutdown of the output module 161 shorts the electrodestogether and connects them to ground through one of the current sources.Normally, this is a desirable and safe condition. However, certainfailures could cause current to flow after shutdown, resulting in damageto the nerve. To eliminate this problem, an additional check can be madeafter normal shutdown has been completed. If current flow is detected,the leads are disconnected from each other (allowed to float) and thecurrent sources are programmed to zero current.

7. Auto-Increment Therapy Delivery

For blocking therapy to be effective, energy delivery may need to beincreased beyond the level that a patient perceives as acceptable at theinitiation of therapy. The power of the therapy signals can be increasedin small increments to enable the patient to acclimate to the morepowerful therapy signals.

For example, the current of the therapy signal can be increased in stepsof about 1 mA at weekly follow-up visits. Over time, patients maywillingly accept multiple increments of 1 mA/week through periodicfollow-up visits and programming sessions. For example, an initialsetting of 3 mA may rise to at least 6 mA as a result of such follow-upsessions.

In certain embodiments of the therapy system 100, energy (i.e., power)delivery can be incrementally increased or decreased automatically overa pre-determined period of time. Advantageously, this automaticincremental increase can mitigate the need for frequent doctor officevisits. This flexibility is especially convenient for patients who arelocated remote from the implanting bariatric center.

In an embodiment, the therapy system 100 automatically increases thecurrent of the therapy signal by, for example, 0.25 mA every other day,cumulatively achieving the 1 mA/week incremental increase. In anotherembodiment, the therapy system 100 increases the current by about 0.125mA per day. Initial studies have demonstrated such increment levels asacceptable.

The patient can retain the ability to turn therapy off at any time andreturn to the physician for re-evaluation. Alternatively, the patientcan revert to previously acceptable therapy delivery levels (e.g., thetherapy level of the previous day). For example, the patient caninteract with the external charger 101 to issue such an instruction.

The physician can choose whether to activate the auto-increment therapycapability. The physician also can specify the date and/or time oftherapy initiation and therapy parameters (e.g., including the startingand ending therapy parameters). The physician also may specify safetylimits or tolerances for the therapy parameters. Additionally, thephysician can specify the rate at which the therapy parameters areincremented over various time periods (e.g., about 0.5 mA/day for thefirst 7 days, then 0.125 mA/day over the following 24 days).

8. Predetermined Programs

One or more therapy programs can be stored in the memory of the externalcomputer 107. The therapy programs include predetermined parameters andtherapy delivery schedules. For example, each therapy program canspecify an output voltage, a frequency, a pulse width, ramp-up rates,ramp-down rates, and an on-off cycle period. In an embodiment, theramp-up rates and ramp-down rates can be individually and separatelyprogrammed.

In use, the physician may select any one of these therapy programs andtransmit the selected therapy program to the implanted neuroregulator104 (e.g., via the external charger 101) for storage in the memory ofthe neuroregulator 104. The stored therapy program then can control theparameters of the therapy signal delivered to the patient via theneuroregulator 104.

Typically, the parameter settings of the predetermined programs are setat the factory, prior to shipment. However, each of these parameters canbe adjusted over a certain range, by the physician, using the computer100 to produce selectable, customized, predetermined therapy programs.Using these selectable, customized therapy programs, the physician canmanage the patient's care in an appropriate manner.

For example, when patients require more varied therapies, theneuroregulator 104 can store a therapy program including one or morecombinations of multiple therapy modes sequenced throughout the day.

For example, referring to electrode configuration shown in FIG. 10, asingle therapy program can include instructions to apply a blockingsignal between electrode tips 212 (anterior vagal nerve) and 212 a(posterior vagal nerve) from 8 a.m. to noon at 6 mA and kHz; alternatingbetween applying a blocking signal to posterior tip 212 a to ring 218 aand applying a blocking signal to anterior tip 212 to ring 218 from noonto 2 p.m. at 3 mA and 2.5 kHz; and applying a blocking signal fromelectrode tip 212 to electrode tip 212 a from 2 p.m. from 2 p.m. tomidnight at 6 mA and 5 kHz.

9. Operation Logs

In general, the neuroregulator 104 can have a time base to facilitatethe delivery of therapy according to the treatment schedule. Todetermine this time base, the neuroregulator 104 can maintain one ormore operating logs indicating the operations of the therapy system 100.

For example, the neuroregulator 104 maintains a time-and-date-stampeddelivery log of the actual delivery of therapy. For example, thedelivery log can include the time and date of initiation of each therapyepisode, the time and date of completion of the therapy episode, thetherapy parameters associated with the therapy episode. Both scheduledtherapy and automatically-initiated therapy can be logged. The deliverylog also can include a parameter to indicate whether the therapy episodewas scheduled or automatically initiated.

Additionally, the neuroregulator 104 can maintain atime-and-date-stamped error log of all conditions that interfered withthe delivery of therapy. For example, the error log can record allimpedances measured, temperatures measured by the on-board temperaturesensor, each instance in which the battery was charged by the externalcharger 101, each instance in which the battery reached its low-chargethreshold, and each instance in which the battery reached its depletedthreshold.

The delivery log and the error log are readable by the external computer107 (e.g., a clinician programmer). In an embodiment, the delivery logand the error log each can accommodate up to about 3 months of data.

10. Detection of Food Passage Through the Esophagus

Neural blocking therapy can affect the rate at which the stomach emptiesand the level of intestinal motility. When applying neural blockingtherapy for obesity control, it is desirable to determine theapproximate times at which the patient ingests food (i.e., mealtimes)and the approximate quantity of food being consumed at each meal.Advantageously, with this information, the duty cycle of the therapysystem 100 can be synchronized with the mealtimes. Additionally, thenature of the therapy can be adjusted in accordance with the quantity offood being consumed. For example, food detection is described in U.S.Pat. No. 5,263,480 to Wernicke et al, issued Nov. 23, 1993, thedisclosure of which is hereby incorporated herein by reference.

In certain embodiments of the therapy system 100, the anterior andposterior vagal nerve electrodes 212, 212 a can be positioned on theesophagus E adjacent to the junction between the esophagus E and thestomach. An impedance measurement between the anterior and posteriorvagal nerve electrodes 212, 212 a provides a measure of the presence offood in the esophagus E between the electrodes 212, 212 a (e.g., seeFIG. 11). The time integration of this impedance value provides ameasure of the quantity of food consumed.

The impedance value between the electrodes 212, 212 a can be measured bypassing a low amplitude, sinusoidal signal (e.g., having a frequency ofabout 500-1000 Hz) between the electrodes 212, 212 a. In an alternativeembodiment, the impedance can be measured by passing the signal betweenthe ring electrodes 218, 218 a. In other embodiments, the dual bipolarlead/electrode configuration can operate as a quadripolar array.

In a quadripolar electrode array, two pairs of electrodes are typicallysecured in generally the same plane and normal to the length of theesophagus E. In such a configuration, a small signal applied across onepair of the electrodes (e.g., tip electrode 212, ring electrode 218) canbe detected across the other pair (e.g., tip electrode 212 a, ringelectrode 218 a). In general, changes in relative amplitude of thedetected signal are proportional to changes in resistance of the signalpath.

The impedance of the signal changes when food progresses down theesophagus E. This impedance change causes the amplitude of the detectedsignal to change, thereby providing an indication of the fact that foodhas passed, and giving an indication of the quantity of food. While abipolar electrode pair may be used for both signal application andsensing across the esophagus E, it has the disadvantage of someinterference as a result of polarization potentials.

More generally, this technology can be used to detect changes in thenature of the fluid within a vessel or lumen of the body. Suchtechnology can be utilized in multiple applications. For example, thisimpedance measurement technology can be used to detect the presence ofliquid/food in the distal esophagus to ascertain the presence ofesophageal reflux.

In another embodiment, this impedance measurement technology can be usedin diagnosing eating abnormalities, such as bulimia.

In one embodiment, the time history of the transesophageal impedancemeasurement is recorded in the memory of the implanted module (e.g., inan operating log), for later telemetry to the external module, forreview and analysis by the physician. With this information, thephysician can preferentially choose the operating parameters of thesystem to best suit the eating habits of an individual patient.

In an alternative embodiment, the output of the transesophagealimpedance measurement becomes a control input into CPU 154 of circuit112 in neuroregulator 104 (FIG. 3). The therapy signal output of theneuroregulator 104 can be timed automatically to correspond to thetiming and quantity of food consumed via a suitable algorithm.

11. Activity Monitoring System

The weight reduction resulting from the application of therapy describedin this patent application is expected to produce an increased feelingof well-being in the patient, and possibly an increase in the amount ofactivity in which the patient is comfortable becoming involved.

In certain embodiments, the therapy system 100 monitors the activity ofthe patient. Generally, the therapy system 100 records the change inactivity over the course of treatment. The therapy is applied toaccomplish a goal (e.g., obesity reduction), and the activity level as aconsequence of achieving the goal (e.g., weight loss) is then measured.

In an embodiment, this change in activity then can be mapped to theaffects of the treatment. This mapping of the change in activity to theresults of treatment can be personally advantageous to patients as wellas advantageous to the medical community. For example, knowledge of thelikely change, both in weight and in activity level, could be usefulinformation for patients who are contemplating the implant andassociated therapy.

In addition, such mapping would advantageously provide documentedevidence of the positive effect of the weight control system toreimbursement groups. Additionally, from a medical/scientificperspective, it is known that weight loss is generally related tocaloric intake, activity level, and metabolic rate. Increasedquantification in the area of activity level would aid in developing arobust relationship among these factors.

There are a variety of methods which can be used for measuring activitylevel. Some of these models have been used as the basis for determiningthe preferred rate of implantable pacemakers and defibrillators. Forexample, a sensor of movement or acceleration (e.g., a gyroscope-basedsensor), can provide an instantaneous measurement of activity level.Suitable hardware, software, and/or algorithm systems can then derivefrom these measurements the activity level averaged over a period oftime (e.g., a 24 hr period).

An accelerometer also can be used to track patient activity. Otherexamples of activity sensing options include tracking the respiratoryrate of the patient, by monitoring bio-impedance measurements (e.g.,intrathoracic impedance), measuring a minute volume of, e.g., acompendium of respiratory rate and tidal volume, and monitoring bloodpH, blood oxygen level, and blood pressure. In each case, theinstantaneous value of the measurement can be integrated over a suitabletime period.

With the foregoing detailed description of the present invention, it hasbeen shown how the objects of the invention have been attained in apreferred manner. Modifications and equivalents of disclosed conceptssuch as those which might readily occur to one skilled in the art areintended to be included in the scope of the claims which are appendedhereto.

1. A system for applying therapy to an internal anatomical feature of apatient comprising: an external component including an external antennaconfigured to be placed above a skin layer of a patient, the externalcomponent including a memory in which therapy programs and therapyschedules can be stored, the external component also including a userinterface configured to receive input from a user and to display outputto the user, the input including a selection of one of the therapyprograms and one of the therapy schedules; and an implantable componentfor placement in the body of the patient beneath the skin layer, theimplantable component including an implanted antenna configured tocommunicate with the external antenna across the skin layer throughradiofrequency communication, the implantable component configured toreceive the selected therapy program and the selected therapy schedulefrom the external component via the external and implanted antennas, theimplantable component being adapted to be selectively configured intoone of a training mode and a delivery mode, the implantable componentconfigured to apply therapy to the internal anatomical feature inaccordance with the selected therapy program and the selected therapyschedule when configured in the delivery mode, and the implantablecomponent configured to simulate application of therapy when configuredin the training mode and to not apply therapy.
 2. The system of claim 1,further comprising at least one electrode configured to be implantedwithin a body of the patient beneath the skin layer and adjacent theanatomical feature, the electrode being communicatively coupled to theimplantable component and being configured to apply therapy to theanatomical feature when instructed by the implantable component when theimplantable component is configured in the delivery mode.
 3. The systemof claim 2, wherein the implantable component instructs the electrode toapply a non-therapy signal to the anatomical feature when theimplantable component is configured in the training mode.
 4. The systemof claim 1, wherein the implantable component is configured to applytherapy according to a second therapy program when the second therapyprogram is selected at the external component and transmitted from theexternal component to the implantable component if the implantablecomponent is configured in the delivery mode.
 5. The system of claim 1,wherein the implantable component sends data to the external componentindicating whether the treatment is being delivered according to theselected therapy program and the selected therapy schedule when theimplantable component is configured in the delivery mode.
 6. The systemof claim 1, wherein the implantable component is configured to not applytherapy according to a second therapy program when the second therapyprogram is selected at the external component and transmitted from theexternal component to the implantable component if the implantablecomponent is configured in the training mode.
 7. The system of claim 1,wherein the implantable component sends dummy data to the externalcomponent when the implantable component is configured in training mode,the dummy date appearing to indicate whether the treatment is beingdelivered according to the selected therapy program and the selectedtherapy schedule.